(a) Technical Field
The present invention relates to a fuel cell stack manifold supplying and distributing hydrogen, air, and cooling water for operating a stack, and more particularly to a fuel cell stack manifold including an ejector for recirculating a stack exhaust gas.
(b) Background Art
In general, a fuel cell is a kind of power generator that converts the chemical energy of fuel into electric energy not by changing it into heat through combustion, but by electrochemically reacting it in a fuel cell stack. Such fuel cells can be used not only for supplying power for industry, homes, and vehicles, but also for supplying power to small electric/electronic products, particularly portable devices.
Automotive fuel cell systems generally include a fuel cell stack that generates electric energy, a fuel supply device that supplies fuel (e.g., hydrogen) to the fuel cell stack, an air supply device that supplies the hydrogen in the air which is an oxidizer for electrochemical reaction to the fuel cell stack, and a cooling system that removes the heat from the reaction of the fuel cell stack to an outside environment of the system and controls the operation temperature of the fuel cell stack.
Recently, typically a polymer electrolyte membrane fuel cell having high power density in fuel cells is used an automotive power source. Such a polymer electrolyte membrane fuel cell includes a membrane electrode assembly with a catalyst electrode layer, where an electrochemical reaction occurs, attached to both sides of a solid polymer electrolyte membrane through which hydrogen ions move, a gas diffusion layer that uniformly distributes a reaction gas and transmits generated electric energy, a bipolar plate that moves the reaction gas and cooling water along a reaction channel, and a gasket and a fastening mechanism that maintains airtightness for the reaction gas and the cooling water and appropriate fastening pressure.
Further, fuel cell stacks typically have a manifold that forms the inlet channel and the outlet channel of the stack. Manifold provide channels that the gases before and after a reaction and the cooling water flow in/out of.
These manifolds typically have long and complicated internal channels that that allow cooling water and gases to pass therethrough. When a plurality of stack modules are mounted on a fuel cell vehicle, the manifolds attached to the outer sides of the stack modules supply reaction gases (air and hydrogen) and cooling water to the stack modules, respectively. That is, a stack manifold is attached to an outer side of a fuel cell unit module and supplies fluid to a stack or restores it.
Channels through which fluids, that is, hydrogen and air (oxygen) and cooling water or cooling a stack, which are used in a stack, flow are formed in a stack manifold so that the fluids can be supplied to a fuel cell unit module or restored from it via the channels.
Fuel cell systems are also usually equipped with a recirculation system for re-supplying gases discharged from a stack, and to this end, a pump mechanism such as a recirculation blower and an ejector is often used.
For example, in fuel cell systems, it is required to supply hydrogen and oxygen in order to generate a current in a stack. When only the amount of hydrogen to be reacted in a stack is supplied, a sufficient reaction is not generated due to the deficit of density of hydrogen at the end of the reaction surface and uniformity of the fuel supplied to the stack decreases, such that the performance and stability of the stack may be deteriorated, and fuel is excessively supplied.
However, when the fuel remaining after a reaction is discharged, the fuel efficiency of a vehicle decreases, so it has been proposed to apply a recirculation technology of improving fuel efficiency by mixing the gas discharged from the anode of the stack with hydrogen sent out of a tank by recirculating the gas, and by supplying the mixture back to the stack.
Further, when the gas discharged from the stack is recirculated, the electrolyte membrane in the stack can be prevented from drying out by the moisture in the recirculated gas.
A pump circulating a gas is required to recirculate the gas discharged from the stack and hydrogen is recirculated usually by a recirculation blower (using a motor) and an ejector.
Various types of stack manifolds including an ejector for a recirculation system have been disclosed in Korean Patent Application Publication No. 2009-0094904, 10-2012-0136708 etc.
However, those conventional recirculation systems are problematic in that the volume and weight of the system increases and the structures are complicated, because there are needs of channels and members for attaching a pumping mechanism to a stack manifold.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.